North Korea's food shortages are worsening, with a drop in aid and a jump in food prices prompting a "rapid" rise in malnourished children and putting millions of others at risk, two United Nations agencies warned Thursday.

The country faces a shortfall of as much as 700,000 metric tons of food this year, which could affect one-fourth of its 24 million people, Hiroyuki Konuma, the Food and Agriculture Organization's Asia representative, said Thursday in Bangkok. Former President Jimmy Carter accused the United States and South Korea in April of a "human rights violation" for refusing to give food aid to North Korea.

While a harsh winter and summer floods damaged crops, agricultural output is expected to remain about the same or slightly higher than last year, Konuma said. A slump in trade and aid amid U.S.-led efforts to stem funding for Kim Jong Il's government, together with global food prices that remain close to record highs, have meant the North Korean government has been unable to bridge the shortfall, he said.

"We are afraid that next year will be a more severe situation," Konuma said.

South Korea and the United States have resisted U.N. appeals to provide food to North Korea, which they blame for attacks last year that killed 50 South Koreans.

The Obama administration says sanctions aimed at cutting the flow of revenue to the North have to be enforced until Kim meets commitments made in multinational talks to dismantle his nuclear weapons program.